In the field of dentistry, restoration of a patient's tooth or teeth that, for example, have been affected by caries generally includes the replacement of the natural tooth substance by an artificial substance. For larger restorations, pre-finished dental prostheses (such as inlays, crowns and bridges) are commonly used to replace at least a part of the tooth or teeth. The tooth to be repaired will be referred to only as a single tooth for simplicity, although it is possible that multiple teeth may be restored as part of the same procedure.
To restore a tooth, the dentist usually completely removes the decayed tooth material, and prepares the remainder of the tooth to receive a dental prosthesis. For example, if a crown will be used for the intended dental restoration, the tooth stump is commonly prepared so that it can be fitted with the crown using an adhesive.
The teeth of the patient are then usually replicated by taking an impression, and using the impression to make a plaster model. The model can be used to make, for example, a suitable dental prosthesis in a dental laboratory.
In recent years, dental prostheses have been produced using automated manufacturing processes such as milling or grinding. There are machines on the market for producing crowns and bridges and/or a precursor of it (herein generally referred to as dental workpiece) machined from a material blank by an automated process. For example, a system allowing computer controlled manufacturing of dental workpieces is available under the designation Lava™ CAD/CAD System, from 3M ESPE AG, Germany.
Typically the automated production of a dental prosthesis comprises the following steps.
First, a suitable system captures of the shape of the tooth or teeth of the patient. This can be done by scanning the plaster model of the patient's teeth, or alternatively by scanning the actual teeth in the patient's mouth. The scan data is normally used to create a virtual model of the prosthesis using software, for example computer-aided design (CAD) software. The software may provide data for computer-controlled manufacturing of a dental workpiece, for example the instruction data for controlling a milling or grinding machine.
In a second step, a milling or grinding machine machines the dental workpiece using the instruction data. The instruction data may be obtained from one of the steps mentioned above or otherwise, for example from a database comprising standard instructions for machining standard shapes. When machining the dental workpiece from the blank, the blank is normally affixed in a support frame and the support frame is held in position. This allows the dental workpiece to be positioned precisely during the machining operation. Usually the workpiece is connected to the remainder of the blank by webs to ensure that it is held in place during the machining operation. Typically the webs are rather small structures, so that the workpiece can be machined precisely without having the machine interfere with the webs. On the other hand, the webs are preferably big enough so that they can hold the workpiece securely in place during machining. When the workpiece has been fully machined, the webs are usually manually cut to separate the workpiece from the rest of the blank.
In a third step, the workpiece may be finally polished, or provided with a veneer, to form the finished prosthesis.
A prosthesis made based on a computer-controlled machined workpiece is generally very precise and can usually be applied to the prepared tooth or teeth by the dentist without extensive adaptation. The prosthesis usually consists of a very durable and biocompatible material, and it is affixed to the prepared tooth using an adhesive.
DE 298 15 486 U1 discloses a device for producing a dental workpiece having a blank and a support body. The blank is accommodated within a recess of the support body. The support is designed so that the blank does not extend beyond the support body in any direction.
In US 2003/0132539 a device for automated production of dental workpieces is disclosed. A blank is inserted into a support. The blank is linked with only opposite inner walls of a recess provided within the support. A gap is left between the blank and the other walls. The design is supposed to avoid tensions and micro-cracks within the blank material.